The present invention relates to the purification of methanol containing iron pentacarbonyl impurities.
Methanol, particularly that produced by the reaction of carbon monoxide and hydrogen, generally contains small amount of iron pentacarbonyl as an impurity. The iron pentacarbonyl is apparently formed by reaction of iron present during the reaction, either in the catalyst or the reactor system itself, with carbon monoxide. The usual crude methanol, such as that produced by reaction of carbon monoxide and hydrogen, also generally contains various other impurities such as water, ethanol and the like which must be removed. Various systems have been devised to effect the removal of impurities from a crude methanol.
For example, U.S. Pat. No. 3,373,180 issued Mar. 12, 1968, to John Arnold Glass and Wilbert H. Urry and U.S. Pat. No. 3,433,841 issued Mar. 18, 1969, to John S. Dehn and John Arnold Glass disclose the removal of iron pentacarbonyl impurities by passing methanol through an ion exchange resin loaded with various metal ions. During the passage through the ion exchange resin, the iron of the iron pentacarbonyl (which is in a zero valent state) is oxidized to the ferrous state and retained on the resin bed. Such method is disadvantageous in that it involves the use of expensive ion exchange resins, and also in that it does not remove such impurities as waer and ethanol, thus necessitating another purification step to purify a crude methanol containing such other impurities.
The most widely used method of purifying a crude methanol is by distillation. In such a distillation, the volatile iron pentacarbonyl (which forms an azeotrope with methanol which is more volatile than methanol) is removed overhead and the methanol as bottoms. However, where distillation is utilized to purify a crude methanol containing iron pentacarbonyl impurities as well as high boiling impurities (that is higher boiling than methanol) such as water and ethanol, at least two distillation towers are required. That is, one distillation tower is required for removing the iron pentacarbonyl as light ends and another for removing the high boiling impurities. While the two-step distillation is effective, it would obviously be more desirable and more economical to effect the removal of the iron impurities as well as the high boiling impurities in a single distillation.
It is thus an object of the present invention to provide an improved method for removal of iron pentacarbonyl impurities from methanol. It is a further and particular object of the present invention to provide a method for purification of a crude methanol containing iron pentacarbonyl impurities as well as high boiling impurities involving only a single distillation step. It is a special object of the present invention to provide a method for purification of such a crude methanol which has been produced by the reaction of carbon monoxide and hydrogen. Additional objects will become apparent from the following description of the present invention.